A man wrote to me about this problem with his baby who developed a problem unique to 5 alpha reductase inhibitors
This is what Merck wrote:
Although the above comments reference 2 studies using a 5?mg dose, Merck (2007) also measured semen levels of finasteride in patients taking a 1?mg dose. The men were treated with 1 mg for 6 weeks. The highest level measured was 1.52 ng/mL, and the mean level was 0.26 ng/mL. Using the highest measured level (1.52 ng/mL), women exposed to a 5?mL ejaculate per day would be exposed to 7.6 ng/d (assuming 100% vaginal absorption). Merck (2007) found this level to be 750 times lower than the “no effect” level for developmental abnormalities in rhesus monkeys.
In summary, a 1?mg dose of finasteride does not appear to adversely affect spermatogenesis. In addition, the level present in the ejaculate of patients taking 1 mg appears to be negligible. Thus, there does not appear to be any need to stop 1 mg of finasteride in those patients trying to conceive or in those whose partners are pregnant.
This is what is really the issue: